Generally, in a transmission type X-ray generator which emits electrons at a transmission target and makes an X-ray be generated, X-ray generation efficiency is significantly low. When electrons are accelerated to high energy and emitted at the transmission target to make an X-ray be generated, the ratio of energy of electrons that becomes the X-ray is only 1% or less of the entire electrons colliding with the transmission target: the rest, about 99% or more, of the electrons becomes heat. Therefore, improvement in X-ray generation efficiency is required. When the electrons collide with the transmission target, reflected electrons are generated. It is known that the reflected electrons do not contribute to generation of the X-ray.
PTL 1 discloses an X-ray tube with improved X-ray generation efficiency. X-ray generation efficiency is improved in the following manner: an anode member provided with a conical channel of which opening diameter is reduced from an electron source toward a target is disposed between the electron source and the target; and electrons are made to be elastically scattered on a channel surface and enter the target.
PTL 2 discloses a transmission X-ray target in which target metal is formed on a ceramic or glass X-ray transmission window substrate.